Field of the Invention
The present invention relates to a power supply apparatus, which is suitable for controlling a heat fixing device mounted in an image forming apparatus such as an electrophotographic copying machine or a printer.
Description of the Related Art
In an image forming apparatus such as an electrophotographic copying machine or a printer, there is provided a heat fixing device configured to heat and press an unfixed toner image onto a recording material to fix the unfixed toner image on the recording material. In a power supply apparatus configured to control supply of power to the heat fixing device, there has been widely used a method of controlling AC voltage, which is supplied from an AC power supply, using a bidirectional thyristor (hereinafter referred to as “triac”) or the like. As for major functions of the above-mentioned power supply apparatus, the following technologies have been proposed. For example, in Japanese Patent Application Laid-Open No. 2007-212503, there is proposed a technology of detecting a current effective value of current which flows to the heat fixing device, to thereby detect power supplied to the heat fixing device. Further, for example, in Japanese Patent Application Laid-Open No. 2013-123348, there is proposed a technology of detecting an accurate zero cross timing of an AC power supply while reducing power consumption of a circuit for detecting a reference timing (zero cross timing) during a phase control for power supplied from the AC power supply.
With regard to the power supply apparatus, highly accurate power supply control with respect to the heat fixing device is required. Thus, there has been a demand to achieve, at low cost, high calculation accuracy at the time of setting power to be supplied to the heat fixing device and highly accurate power supply timing.